1. Field of the Invention
The present invention relates in general to a diamond-coated tool, and more particularly to such a diamond-coated tool which is capable of machining a workpiece with high degrees of surface smoothness and profile accuracy, and also to a method of manufacturing the same.
2. Discussion of the Related Art
As one type of a cutting tool such as an end mill, a drill, a tap and a disposable or throwaway insert, there is proposed a diamond-coated tool in which a tool substrate is coated with a diamond coating, as disclosed in JP-B2-2519037 (publication of Japanese Patent issued in 1996) by way of example. In the tool disclosed in this Japanese Patent publication, the tool substrate is coated with the diamond coating in accordance with CVD (chemical vapor deposition) method.
The diamond coating of the disclosed tool consists of an aggregation of diamond crystals, each of which has grown or expanded from a nucleus disposed on the surface of the tool substrate so as to have a large columnar shape, so that each diamond crystal has a grain size or diameter as large as 5-10 xcexcm as measured on or adjacent to an outer surface of the diamond coating, i.e., as measured on a plane perpendicular to a direction in which the diamond crystal has grown or expanded. The large diameter of each diamond crystal causes the outer surface of the diamond coating to have large pits and projections and a high degree of surface roughness (e.g. a large value in the maximum height Ry). The large pits and projection on the diamond coating surface are inevitably transferred onto a machined surface of a workpiece which is machined by the cutting tool, thereby making it difficult to obtain a required degree of smoothness on the machined surface.
It is considered possible to somewhat smooth the diamond coating surface, for example, by grinding a portion of the diamond coating which portion covers the cutting edge, by attaining uniform crystal orientation of the diamond crystals, or by reducing the size of each crystal, namely, forming the diamond crystals in the form of crystallites. However, the grinding operation leads to an increase in a manufacturing cost of the tool, and provides a possibility that the diamond coating is damaged by a shock applied to the tool during the grinding operation, thereby possibly deteriorating a durability of the coating. The uniformity of the crystal orientation in (100) causes a large compressive stress to remain in the coating, thereby possibly causing easy removal of the coating from the substrate of the tool. Further, where the surface of the substrate is roughened to have pits and projections serving to increase an adhesion strength with which the diamond coating adheres to the substrate, the pits and projections, i.e., irregularities on the roughened surface of the substrate are not offset by the diamond crystallites, whereby the pits and projections formed on the substrate surface undesirably remain more or less on the coating surface, resulting in an unsatisfactory degree of smoothness of the coating surface. The cutting edge of the tool is rounded or chamfered in the roughening operation, whereby the cutting sharpness or performance of the tool is deteriorated. The deterioration of the cutting sharpness or performance also constitutes a factor causing the deterioration of the machined surface of the workpiece.
The above-described drawbacks or problems are encountered not only where the diamond-coated tool takes the form of a cutting tool but also where the diamond-coated tool takes the form of other machining tool such as a cold-forming tool which is designed to form the workpiece into a desired shape by plastically deforming the workpiece.
It is therefore a first object of the present invention to provide a diamond-coated tool which is capable of machining a workpiece with high degrees of surface smoothness and profile accuracy. This first object may be achieved according to any one of first, second, third, fourth and fifth aspects of this invention which are described below.
It is a second object of the present invention to provide a method of manufacturing a diamond-coated tool which is capable of machining a workpiece high degrees of surface smoothness and profile accuracy. This second object may be achieved according to any one of sixth, seventh, eighth, ninth and tenth aspects of this invention which are described below.
The first aspect of the invention provides a diamond-coated tool comprising: a substrate; and a diamond coating disposed on the substrate, the diamond coating being formed of diamond crystals grown on the substrate, each of the diamond crystals having a diameter not larger than 2 xcexcm as measured on an outer surface of the diamond coating.
The term xe2x80x9cdiameter of each diamond crystal or each diamond crystallitexe2x80x9d used in this specification is interpreted to mean the largest dimension of each diamond crystal or crystallite as measured in a direction substantially perpendicular to a direction in which the diamond crystal or crystallite has expanded or grown, namely, as measured in a direction substantially parallel to the surface of the substrate and the outer surface of the diamond coating. It is preferable that each of all the diamond crystals or crystallites which are exposed on the outer surface of the diamond coating has a diameter not larger than 2 xcexcm. It is noted that the diameters of the diamond crystals or crystallites can be measured, for example, by using an electron microscope of about 1000-10000 magnification.
According to the second aspect of the invention, in the diamond-coated tool defined in the first aspect of the invention, the diameter of each of the diamond crystals is not larger than 2 xcexcm as measured on any one of cross sections perpendicular to a direction in which each of the diamond crystals has expanded by growth thereof. It is preferable that each of all the diamond crystals which are exposed on the outer surface of the diamond coating has a diameter not larger than 2 xcexcm as measured on any one of the cross sections perpendicular to the direction in which the diamond crystal has expanded in the growth.
According to the third aspect of the invention, in the diamond-coated tool defined in the first or second aspect of the invention, the grown diamond crystals consist of grown diamond crystallite, and the diamond coating consists of a plurality of layers.
The diamond-coated tool defined in any one of the first, second and third aspects of the invention provides a surface of a workpiece machined by the tool, with a high degree of surface smoothness, owing to reduced pits and projections, i.e., reduced irregularities on the outer surface of the diamond coating which is constituted by the diamond crystals each having the diameter not larger than 2 xcexcm as measured on the outer surface of the diamond coating. The diamond-coated tool defined in the third aspect of the invention has an additional advantage that the diameter of each diamond crystal can be easily reduced owing to the multilayer diamond coating consisting of the plurality of layers superposed on each other. It is noted that the term xe2x80x9ccrystallitesxe2x80x9d used in this specification is interpreted to mean ones of the crystals each of which has the maximum diameter and length (the largest dimension as measured in the direction substantially perpendicular to the expanding direction of the diamond crystal and the largest dimension as measured in the expanding direction of the diamond crystal) not larger than about 3 xcexcm.
The fourth aspect of the invention provides a diamond-coated tool comprising: a substrate; and a diamond coating consisting of a plurality of layers and disposed on the substrate, the diamond coating being formed of diamond crystals grown on the substrate, each of the diamond crystals having a length not larger than 2 xcexcm as measured in a direction in which each of the diamond crystals has expanded by growth thereof. It is preferable that each of all the diamond crystals or crystallites which are exposed on the outer surface of the diamond coating has a length not larger than 2 xcexcm as measured in the direction in which the diamond crystal or crystallite has expanded in the growth. The lengths of the diamond crystals or crystallites can be measured, for example, by using an electron microscope of about 1000-10000 magnification.
The diamond-coated tool of this fourth aspect of the invention also provides a surface of a workpiece machined by the tool, with a high degree of surface smoothness, owing to reduced pits and projections in the outer surface of the multilayer diamond coating which is constituted by the diamond crystals each having the length not larger than 2 xcexcm as measured in the expanding direction of the diamond crystal, i.e., in a direction substantially perpendicular to the surface of the substrate.
The fifth aspect of the invention provides a diamond-coated tool comprising: a substrate having a surface roughened to have a predetermined degree of surface roughness; and a diamond coating consisting of a plurality of layers and disposed on the roughened surface of the substrate, the diamond coating being formed of diamond crystals grown on the substrate, each of the diamond crystals having a diameter not larger than 2 xcexcm as measured on an outer surface of the diamond coating, the diamond coating having a maximum thickness of not larger than 14 xcexcm; wherein the roughened surface has a roughness curve whose maximum height Ry is not larger than 1 xcexcm and whose ten-point height of irregularities Rz is 0.2-0.5 xcexcm; and wherein the substrate has a rake face, a flank face and a cutting edge which is defined by an intersection of the rake face and the flank face, the cutting edge being rounded as a result of roughening of the surface of the substrate such that the cutting edge is displaced in an inward direction of the substrate by a distance not larger than 5 xcexcm.
The distance, by which the cutting edge is displaced as a result of the rounding or chamfering of the cutting edge, is represented, for example, by the reference sign xe2x80x9cdxe2x80x9d in FIG. 3 that is a cross sectional view of a diamond-coated tool constructed according to an embodiment of the invention. In FIG. 3, the reference numerals 19xe2x80x2, 19 denote the cutting edge before and after the rounding of the cutting edge, respectively.
In the diamond-coated tool of this fifth aspect of the invention, the displacement amount of the cutting edge as a result of the rounding of the cutting edge is not larger than 5 xcexcm, and the maximum thickness of the diamond coating is not larger than 14 xcexcm. Since the rounding amount of each cutting edge and the thickness of the diamond coating are thus minimized, the tool has an excellent cutting sharpness even after the substrate of the tool has been coated with the diamond coating. Further, the roughened surface of the substrate, which has the roughness curve whose maximum height Ry is not larger than 1 xcexcm and whose ten-point height of irregularities Rz is 0.2-0.5 xcexcm, has a required degree of surface smoothness, while providing a required degree of adhesion strength with which the diamond coating adheres to the substrate. The multilayer diamond coating is formed of the diamond crystals each having the diameter not larger than 2 xcexcm as measured on the outer surface of the diamond coating, so that the outer surface of the diamond coating has a sufficiently high degree of surface smoothness which cooperates with the above-described excellent cutting sharpness for improving the surface smoothness of the machined surface of the workpiece.
The sixth aspect of the invention provides a method of manufacturing a diamond-coated tool which includes a substrate having a surface, and a diamond coating disposed on the surface of the substrate, the method comprising: a nucleus bonding step of bonding nucleuses to the substrate which is disposed in a reactor of a chemical vapor deposition device; and a crystal growing step of growing diamond crystals in the reactor in accordance with a chemical vapor deposition method, such that the diamond crystals expand from the nucleuses, wherein the nucleus bonding step and the crystal growing step are repeatedly implemented for thereby forming, on the surface of the substrate, the diamond coating consisting of a plurality of layers.
According to the seventh aspect of the invention, in the method defined in the sixth aspect of the invention, the diamond crystals are grown for a predetermined time in the crystal growing step, the predetermined time being determined such that each of the diamond crystals grows to have a diameter not larger than 2 xcexcm as measured on any one of cross sections perpendicular to a direction in which each of the diamond crystals expands by growth of the diamond crystals.
According to the eight aspect of the invention, in the method defined in the sixth or seventh aspect of the invention, the diamond crystals are grown for a predetermined time in the crystal growing step, the predetermined time being determined such that each of the diamond crystals grows to have a length not larger than 2 xcexcm as measured in a direction in which each of the diamond crystals expands by growth of the diamond crystals.
The method defined in the sixth or seventh aspect of the invention is advantageously used for manufacturing the diamond-coated tool defined in any one of the first, second and third aspects of the invention, and provides the substantially same technical advantages as the first, second and third aspects of the invention. The method defined in the eighth aspect of the invention, in which the growths of the diamond crystals are suspended at the predetermined time that has been determined such that each diamond crystal grows to have the length not larger than 2 xcexcm, is advantageously used for manufacturing the diamond-coated tools defined in the fourth aspect of the invention, and provides the substantially same technical advantages as the fourth aspect of the invention. In the method defined in any one of the six, seventh and eighth aspects of the invention, the nucleus bonding step and the crystal growing step are repeatedly implemented in the reactor of the chemical vapor deposition device, for forming the diamond coating consisting of the plurality of layers. Thus, the method of this fourth aspect of the invention makes it possible to simultaneously manufacture a large number of diamond-coated tools in each of which the sizes of the diamond crystals are accurately controlled with high precision.
The ninth aspect of the invention provides a method of manufacturing a diamond-coated tool which includes a substrate having a surface, and a diamond coating disposed on the surface of the substrate, the substrate having a rake face, a flank face and a cutting edge that is defined by the an intersection of the rake face and the flank face, the method comprising; a surface roughening step of roughening the surface of the substrate of the tool, such that the roughened surface has a roughness curve whose maximum height Ry is not larger than 1 xcexcm and whose ten-point height of irregularities Rz is 0.2-0.5 xcexcm, and such that the cutting edge is chamfered or rounded to be displaced in an inward direction of the substrate by a distance not larger than 5 xcexcm; and a coating forming step of forming the diamond coating on the roughened surface of the substrate, by growing diamond crystals in accordance with a chemical vapor deposition method, such that each of the diamond crystals has a diameter not larger than 2 xcexcm as measured on an outer surface of the diamond coating, and such that the diamond coating consists of a plurality of layers and has a maximum thickness not larger than 14 xcexcm.
According to the tenth aspect of the invention, in the method defined in the ninth aspect of the invention, the coating forming step includes: a nucleus bonding step of bonding nucleuses to the substrate which is disposed in a reactor of a chemical vapor deposition device; and a crystal growing step of growing diamond crystals for a predetermined time in the reactor in accordance with a chemical vapor deposition method, such that the diamond crystals grow from the nucleuses, wherein the predetermined time is determined such that each of the diamond crystals grows to have a diameter not larger than 2 xcexcm, and wherein the nucleus bonding step and the crystal growing step are repeatedly implemented for thereby forming, on the surface of the substrate, the diamond coating consisting of the plurality of layers.
The method defined in the ninth or tenth aspect of the invention is advantageously used for manufacturing the diamond-coated tool defined in the fifth aspect of the invention, and provides the substantially same technical advantages as the fifth aspect of the invention. In the method defined in the tenth aspect of the invention, the nucleus bonding step and the crystal growing step are repeatedly implemented in the reactor of the chemical vapor deposition device, for forming the diamond coating consisting of the plurality of layers. Thus, the method of the tenth aspect of the invention makes it possible to simultaneously manufacture a large number of diamond-coated tools in each of which the sizes of the diamond crystals are accurately controlled with high precision.
The principle of the present invention is advantageously applicable to a rotary or non-rotary cutting tool such as an end mil, a drill, a tap, a threading die and a replaceable insert which is used to cut, principally, an aluminum casting, an aluminum alloy, a copper, a copper alloy or other non-ferrous metal, and to a method of manufacturing such a cutting tool. However, the principle of the invention is also applicable to a cutting tool which is used to cut a material other than the non-ferrous metal, and even to a non-cutting tool such as a cold-forming tool which is designed to form the workpiece into a desired shape by plastically deforming the workpiece. The substrate of the diamond-coated tool of the invention is preferably made of a cemented carbide, but may be made of a cermet, a ceramic or other material.
While each diamond crystal has the diameter not larger than 2 xcexcm as measured on the outer surface of the diamond coating or as measured on any cross sections perpendicular to the expanding direction of the diamond crystal in the first, second, third, fifth and seventh aspects of the invention, it is more preferable that the diameter of each diamond crystal is not larger than 1 xcexcm in these aspects of the invention. While each diamond crystal has the length not larger than 2 xcexcm as measured in the expanding direction of the diamond crystal in the fourth and eighth aspects of the invention, it is more preferable that the length of each diamond crystal is not larger than 1 xcexcm in these aspects of the invention.
While each diamond crystal has the length not larger than 2 xcexcm in the fourth and eighth aspects of the invention, each diamond crystal in the first, second and third and seventh aspects of the invention may have a length larger than 2 xcexcm as measured in the expanding direction of the diamond crystal as long as the diameter of the diamond crystal is not larger than 2 xcexcm. Where the diamond coating consists of the plurality of layers and is formed of the crystal diamonds whose growths are suspended such that the length of each diamond crystal as measured in its expanding direction is not larger than 2 xcexcm as in the fourth and eighth aspects of the invention, in general, it is possible to prevent the diameter of each diamond crystal from exceeding 2 xcexcm, whereby the pits and projections on the outer surface of the diamond coating can be advantageously reduced. In this respect, the fourth and eighth aspects of the invention may be considered embodied forms of the first, second and third and seventh aspects of the invention. It is also to be understood that the diameter of each diamond crystal in the fourth and eighth aspects of the invention may be larger than 2 xcexcm.
The fifth and ninth aspects of the invention, in which the diameter of each diamond crystal as measured on the outer surface of the diamond coating is not larger than 2 xcexcm, may be considered embodied forms of the first, second and third and seventh aspects of the invention. It is noted that the fifth and ninth aspects of the invention may be modified to include the feature that the length of each diamond crystal as measured in its expanding direction is not larger than 2 xcexcm, in place of or in addition to the feature that the diameter of each diamond crystal as measured on the outer surface of the diamond coating is not larger than 2 xcexcm, as the fourth or eighth aspect of the invention. The modifications provide the same technical advantages as the fifth and ninth aspects of the invention.
In the fifth, ninth and tenth aspects of the invention, the substrate of the tool is subjected to the roughening treatment or step so that the surface of the substrate is roughened for increasing an adhesion strength with which the diamond coating adheres to the substrate. In the other aspects of the invention, however, the substrate surface does not have to be necessarily roughened. For example, it is possible to increase the adhesion strength by providing an interface layer between the substrate and the diamond coating in the other aspects of the invention. That is, in the first, second, third, fourth, sixth, seventh and eighth aspects of the inventions, the diamond coating may be disposed directly on the surface of the substrate, or may be disposed on the interface layer disposed on the surface of the substrate so that the interface layer is interposed between the substrate and the diamond coating. The interface layer may be formed of carbide, nitride or oxide of a metal groups IVa-VIa in the periodic table, or alternatively of aluminum nitride, as disclosed in JP-A-5-263251 (publication of unexamined Japanese Patent Application laid open in 1993) and JP-B2-6-951 (publication of examined Japanese Patent Application laid open for opposition purpose in 1994). The provision of the interface layer has an advantage that it is possible to reliably improve the surface smoothness of the machined workpiece, simply by reducing irregularities such as pits and projections in the outer surface of the diamond coating, irrespective of the surface roughness of the substrate which is covered by the interface layer.
While the thickness of the diamond coating is not larger than 14 xcexcm in the fifth, ninth and tenth aspects of the invention, the thickness of the diamond coating in the other aspects of the invention may be larger than 14 xcexcm.
In the roughening treatment or surface roughening step in the fifth or ninth aspect of the invention, the surface of the substrate is preferably sandblasted or etched in a chemical manner so as to be roughened to have the predetermined degree of surface roughness. If the displacement amount of the cutting edge as a result of the rounding or chamfering of the cutting edge is larger than 5 xcexcm, the cutting sharpness of the tool is deteriorated. The displacement amount of the cutting edge should be accordingly equal to or smaller than 5 xcexcm, preferably, as small as possible, although the optimum displacement amount of the cutting edge varies depending upon the thickness of the diamond coating. The roughened surface should have the maximum height Ry not larger than 1 xcexcm, and the ten-point height of irregularities Rz held in the range of 0.2-0.5 xcexcm. If the maximum height Ry is larger than 1 xcexcm, or if the ten-point height of irregularities is larger than 0.5 xcexcm, the smoothness in the outer surface of the diamond coating is deteriorated due to the large irregularities in the roughed surface of the substrate, resulting in an unsatisfactory degree of smoothness of the surface of the machined workpiece. If the ten-point height of irregularities is smaller than 0.2 xcexcm, on the other hand, it is difficult to reliably obtain a sufficiently high degree of adhesion strength with which the diamond coating adheres to the substrate.
The diamond coating is formed in accordance with, preferably, a microwave plasma CVD method or a hot filament CVD method. However, the formation of the diamond coating may be made in the other CVD methods such as a high-frequency plasma CVD method.